It is called Citadel for two reasons. One is because it is on the level map which is called Citadel, and second is because its a castle. Now your job is to clear it from those nasties and zombies so try it out and save the Citadel.

Credits:

The author of DEEP and HEEP, Probably the best Doom II / Heretic editor. And Id Software for an exelent game.